MEETING REPORT Expert meeting on chikungunya modelling Stockholm, April 2008 www.ecdc.europa.eu ECDC MEETING REPORT Expert meeting on chikungunya modelling Stockholm, April 2008 Stockholm, March 2009 © European Centre for Disease Prevention and Control, 2009 Reproduction is authorised, provided the source is acknowledged, subject to the following reservations: Figures 9 and 10 reproduced with the kind permission of the Journal of Medical Entomology, Entomological Society of America, 10001 Derekwood Lane, Suite 100, Lanham, MD 20706-4876, USA. MEETING REPORT Expert meeting on chikungunya modelling Table of contents Content...........................................................................................................................................................iii Summary: Research needs and data access ...................................................................................................... 1 Introduction .................................................................................................................................................... 2 Background..................................................................................................................................................... 3 Meeting objectives ........................................................................................................................................ 3 Presentations .................................................................................................................................................. 4 Jolyon Medlock: Understanding environmental determinants for the establishment and spread of Aedes albopictus.....4 Francis Schaffner: Entomological aspects related to chikungunya modelling for Europe — the bionomics of Aedes albopictus.................................................................................................................................................................7 Asghar Talbalaghi: Intervention and vector control .................................................................................................. 12 Pierre-Yves Boelle: Investigating a two-wave chikungunya fever epidemic in Réunion Island, 2005–06 ..................... 13 Andrea Pugliese: Modelling approaches in Italy........................................................................................................ 17 Nicolas Bacaer: The basic reproduction number for vector-borne diseases with a periodic vector population.............. 22 Conclusion .................................................................................................................................................... 27 Participants ................................................................................................................................................... 28 References .................................................................................................................................................... 29 Agenda ......................................................................................................................................................... 30 iii Expert meeting on chikungunya modelling MEETING REPORT Summary: Research needs and data access During the course of the expert meeting, entomologists and modelling experts identified the following areas in need of research funding. Additional funding is needed to: • interpret the effects of interventions; • measure the sampling bias associated with mosquito traps in order to assess the actual size of a mosquito population; • develop standardised methods in order to measure mosquito activity during an outbreak; • develop mathematical models which can incorporate mosquito activity as an additional component; and to • develop methods of how to quantify the risk of mosquito importation and establishment in areas where mosquitoes have not been previously present. (ECDC is already funding one project in this area.) All proposed measures are aimed at improving modelling activities that can help to predict chikungunya outbreaks. Data for modelling have to be accurate, accessible, and in the required format. During the outbreaks in Réunion (see page 20), data accessibility was rather spotty. This applies both to data accessibility within Réunion and the data flow between Réunion and other countries. In addition to ensuring that data are accessible, it is important to specify the exact data type that is used for reporting. The data reported from Réunion in 2006 were interpolated data from visits by general practitioners. 1 Expert meeting on chikungunya modelling MEETING REPORT Introduction Following recent outbreaks of chikungunya in Réunion and Italy — the latter outbreak being the first instance of local transmission in continental Europe — it became clear that there is a need for epidemiological models that can be used to predict future outbreaks and at the same time inform public health institutes of impending outbreaks. Some activity is already underway in this area, but research is hampered by insufficient access to data. Also, the research community needs to address methodological approaches and knowledge gaps. Additional research on how outbreak modelling can be used to measure the effects of public health interventions is also required. ECDC organised the April 2008 ‘Expert meeting on chikungunya modelling’ in order to facilitate the discussion between modellers and other experts on chikungunya. In January 2008, leading chikungunya modellers held a teleconference during which it was agreed to organise an expert meeting on chikungunya modelling in order to ensure the exchange of experience on mathematical modelling between experts in chikungunya-affected countries and experts from fields related to vector-borne diseases such as entomology. The aim of the expert meeting in April 2008 was to identify areas for further research at the European level. This meeting report is distributed to external stakeholders and funding agencies in order to inform them about the current state of disease modelling. ECDC activities in this area included an expert consultation on chikungunya risk assessment for Europe (Stockholm, March 2006); on-site visits to the Italian regions affected by chikungunya in 2007; an expert consultation on vector-related risk for Chikungunya virus (CHIKV) transmission in Europe (Paris, October 2007); research aimed at assessing the magnitude and importance of vector-borne diseases in Europe; and a vector risk mapping initiative. 2 MEETING REPORT Expert meeting on chikungunya modelling Background Mathematical modelling of chikungunya started [1] with a computer simulation approach. Some of the more recent papers have focused on different methods for calculating the basic reproduction number R0 within a periodic vector population [2]. Most modelling papers focus on the vector, but there is a noticeable lack of research as far as the inclusion of humans into the mathematical models is concerned. Most of the work in this area is being done in France and Italy, which use different approaches in their calculations [ECDC teleconference, January 2008]. With respect to modelling methods, a vast number of contentious issues exist. Most studies, published and unpublished, have found the value of R0 to be about 3–4. In order to eliminate an outbreak, R0 should be reduced to less than one. One approach is to monitor its value in real time which is particularly helpful when observing the effects of interventions. When mathematically modelling disease outbreaks, a variety of disciplines are involved, ranging from the obvious (mathematics) to entomology and decision making (both for public health and interventions). One problem frequently encountered with R0 is that the same dataset can yield different R0 estimates when different methods are used. This issue needs more attention, both inside and outside the modelling community. The Stockholm meeting in April 2008 had a clear focus on modelling, but in order to get a better look at the knowledge gaps in the area, scientist in related fields were also invited, thus ensuring that their expertise could be incorporated into the existing modelling methods. Meeting objectives In order to discuss how modelling can be used to measure the effects of interventions during an outbreak and estimate the risk of chikungunya establishment in EU Member States, the meeting participants had to: • map and assess different modelling approaches to chikungunya; • agree upon key epidemiological parameters and model structures for modelling chikungunya outbreaks in Europe; • ensure that entomological knowledge was incorporated into the modelling approaches; and • discuss which kind of data is to be collected from future outbreaks and how it will be shared with modellers. The second objective was to identify knowledge gaps in areas that require more research. 3 Expert meeting on chikungunya modelling MEETING REPORT Presentations Jolyon Medlock: Understanding environmental determinants for the establishment and spread of Aedes albopictus The presentation focused on: • work ongoing in the ECDC TigerMaps project; and • published work by the British Health Protection Agency (HPA), funded by a grant-in-aid from the British government. The key question currently addressed in the United Kingdom is if Aedes albopictus can be imported and if it can become established in the British climate. If the mosquito can be established, can it be active for a sufficient period of the year to